UK : What happens at the beginning of a new parliament?

The Houses of Parliament

Following a general election, it usually takes between a week and 10 days after polling day a for MPs to complete the formalities necessary before the Commons can begin substantive business. These formalities including the election of a Speaker and the taking of oaths and affirmation. MPs are due to meet for the first time and elect a Speaker on 9 July – five days after the 2024 election – and it will then take several days for them to be sworn in.
When does a new parliament begin?
A parliament lasts between one general election and the next. Prior to a general election, the existing parliament is formally dissolved and ceases to exist. Following the election, a new parliament begins.
The date on which the new parliament will meet is set out in advance of the general election, in a proclamation issued by the King, on the advice of the government, following dissolution.
How long does it take to get a new parliament up and running?
It varies. This partly depends on how soon the parliament is due to meet following an election, as well as how long it takes parliament to get through certain procedures it is required to undertake before it can get down to business. There are no formal requirements about how long any of this takes.
What happens at the beginning of a new Parliament?

Usually, there are at least a few days between a general election and the date on which parliament is summoned to return. For the last two elections:
2019: two working days between election day (12 December) and parliament’s return (17 December)
2017: two working days between election day (8 June) and parliament’s return (13 June)
2015: seven working days between election day (7 May) and parliament’s return (18 May).

What happen when a new parliament meets for the first time?
The Commons must first elect a Speaker and complete the swearing in of MPs and peers. Once these things have happened a King’s Speech can take place, followed by a debate on the Address (effectively, a debate on the content of the King’s Speech). This is the first substantive business that a new parliament debates and is the first opportunity for a new government to demonstrate that it has the confidence of MPs.
This is a different process from the beginning of a new parliamentary session – the parliamentary ‘years’ that a full parliament is broken down into. Although a King’s Speech is held at the beginning of each session, there is no need for a Speaker election or for members to be sworn in.
How does the election of the Speaker work?
This is the first thing MPs need to do when they return to Westminster after a general election. The process begins on the first day that parliament returns, with MPs formally invited by the King to elect a Speaker. Black Rod – the King’s representative in the House of Lords – is dispatched from the House of Lords to summon MPs to the Lords Chamber, where the Commissioners – members of the Lords, acting in the name of the King, direct MPs to return to the Commons and elect a Speaker.
If the Speaker from the previous parliament has been returned as an MP to the new parliament, and wishes to continue as Speaker, then an MP will move a motion calling for them to be returned to the chair as Speaker. This motion is voted on immediately, without debate. If the motion is passed, the Speaker is re-elected.
However, if the previous Speaker has stepped down or not been returned as an MP, or if MPs decline to re-elect them, then a new Speaker must be elected. This election takes place the following day, through an exhaustive ballot process.
Once a new Speaker is elected, they must be formally approved in the role by the King. Once again, Black Rod is dispatched to summon the Speaker-elect and MPs to the Lords, where the Commissioners inform the Speaker-elect of the King’s approval.

How are MPs and peers sworn in?
The law requires all MPs and peers to take an oath, or make an affirmation, to the King. Members who refuse to do this are not eligible to take their seats in parliament, under the terms of the 1866 Parliamentary Oaths Act.
In the Commons, MPs begin to take their oaths once the Speaker has been elected. Two to three days are usually set aside for this purpose, which takes place before the State Opening of Parliament and the King’s Speech. Most MPs take the oath during this period, although some additional time is set aside in subsequent sitting days for any remaining MPs to be sworn in.
MPs take the oath in order of seniority: the Speaker goes first, followed by the Father of the House (the longest serving male MP), members of the Cabinet and shadow Cabinet, any MPs who are privy counsellors, and then other MPs based on when they were first elected. MPs make their oath or affirmation at the Table of the Commons, in the centre of the chamber – the place specified in law for this purpose.
The process is similar in the House of Lords. Two to three days are set aside for peers to take the oath, and some additional time is also reserved in subsequent sitting days for remaining peers. As in the Commons, peers make their oath or affirmation in order of seniority: beginning with the Lord Speaker, and then archbishops, party leaders, and other members.
Can MPs take part in debates and votes if they have not been sworn in?
No. MPs cannot participate in substantive business in the chamber, including debates or votes, until they have been sworn in. Under the terms of the 1866 Act, MPs who break this rule face a fine of £500 (the same amount as originally set in 1701) and will automatically vacate – or lose – their seat. MPs are also not eligible to receive their salary until they are sworn in.
MPs are only required to be sworn in if they wish to take up their seat. For political reasons, MPs elected from the Sinn Féin party have historically never taken up their seats.
Could these processes happen faster?
Yes – if it was clear immediately following an election that a government could be formed, and if political parties, the Speaker, and the King agreed, then the Commons may be able to get through the necessary formalities and begin its business on the Monday afternoon following a Thursday election – in other words, within three working days of a general election.
In a 2015 report, the Commons Political and Constitutional Reform Committee outlined what an expedited process for the start of a new parliament could look like:
On the first day the Commons returned after an election – the day MPs elect a Speaker – the start of the parliamentary day could be brought forward a few hours (this would require a change to the relevant parliamentary rules prior to dissolution).
The number of visits that MPs are required to make to the Lords as part the process of electing and approving a Speaker could be reduced – by a privy counsellor being dispatched to MPs with a message from the King giving them permission to elect a Speaker. This change to process would likely require the agreement of the King.
The process of swearing in MPs could be accelerated, for example by swearing in MPs at the Table of the Commons in two lines either side of the table, rather than one. Arrangements for the swearing in of MPs are up to the Speaker.
Following is the link of HANSARD SOCIETY on same subject :

https://www.hansardsociety.org.uk/publications/briefings/back-to-business-2024?utm_source=HansardSociety